Biochemistry of water-logged soils: Part I. The effect of water-logging on the different forms of nitrogen, on the reaction, on the gaseous relationships, and on the bacterial flora

Abstract

Rothamsted and Indian soils were water-logged in the absence of freshly decomposing organic matter. Nitrogen changes: Water-logging resulted in: (1) A distinct increase in the free and saline ammonia content. (2) A significant though only slight diminution in the nitric nitrogen. (3) No marked loss of ammonia by volatilisation or otherwise in the gaseous form: nor considerable variation in the nitrites: nor any observable diminution in the total nitrogen. Reaction: Water-logging resulted in an increase in alkalinity; the increase in pH value was closely correlated with the corresponding increase in ammonia. Gaseous relations: Water-logging resulted in: (1) No release of any soluble reducing matter capable of absorbing dissolved oxygen. (2) No appreciable carbon dioxide production. (3) An absorption of dissolved oxygen from the surface water. An equation has been worked out expressing the concentration gradient of dissolved oxygen with depth. Bacterial numbers: From bacterial counts on water-logged soils it was found that: (1) There was significant though slight decrease in bacterial numbers on Thornton's Agar. (2) Very few colonies were obtained by plating aerobically (and fewer still anaerobically) on Giltay's Agar. None of the organisms appearing on the plates brought about any nitrate reduction in soils. (3) The total counts on gelatine plates also showed some decrease. The numbers of gelatine-liquefiers on the other hand did not vary. There was no evidence to suggest that the increased production of ammonia was due to the activity of the gelatine-liquefiers. Agency responsible for ammonia formation: The results indicate that the formation of ammonia in water-logged soils is not due to biological action. It is suggested that the action is due to an enzyme.